Thermogravimetry as a tool for measuring of fracturing fluid absorption in shales

Abstract

Water-based fracturing fluids are used for gas shale stimulations. The fluids are pumped under pressure into the well to create conductive fractures in hydrocarbon-bearing zones. The chemical additives vary depending on the geological and technical conditions of the well. One of the requirements of good fluid coherence is its low absorbency relative to the formation rock. Standard water absorption tests for rocks are usually performed on cubic samples (50 9 50 9 50 mm) soaked in water. In case of rocks which are drilled from the borehole, obtaining such large samples is very difficult; therefore, an attempt was made to determine the rock absorption on small samples, using the TG analysis. Thermogravimetric (TG/DTG) experiments were conducted in temperature range 40-300°C in synthetic air environment. Shale rock samples were soaked in water and fracturing fluid. The absorption of the rocks is related to the shale's mineral composition, which was also determined by thermal analysis (TG/DSC).

Research on the Shale Reservoir Sensitivity by Using the Mineral Analysis Method

“…Damage to oil and gas reservoirs is essentially a decrease in permeability caused by changes in the pore structure of the rock. − Diagnosis and determination of damage mechanisms need to be based on core analysis, sensitivity assessment, working fluid damage simulation experiments, and field evaluation. − Specific aspects, types, and processes of damage occurrence are revealed through comprehensive analysis. − A large number of scholars believe that the intrusion of working fluid filtrate is the main damage factor in low permeability tight gas reservoirs. − The permeability of the core matrix in such gas reservoirs is very low, and the median radius of the throat is less than 1 μm, showing high capillary force characteristics. − The initial water saturation of the reservoir is often lower than the bound water saturation, leading to easy retention of the working fluid filtrate intruding into the core and difficult to flow back, which can easily lead to a significant reduction in the gas permeability and the formation of serious water-phase trap damage. − When drilling in the reservoir section, the reservoir damage originates from drilling fluid leakage or filtration under the effect of positive differential pressure in the wellbore and capillary forces. − Intrusion into the solid phase can cause reservoir fractures and pore throat plugging, while intrusion into the liquid phase is prone to sensitivity damage and water-phase trap damage. − The depth of drilling fluid intrusion and the degree of damage increase with the increase of positive differential pressure in the wellbore and drilling time. − Among them, as an important development direction of oil and gas wells, it is crucial to study the damage factors and extent of horizontal wells. − Horizontal wells are an important means to increase the production capacity of oil and gas wells, but in many cases, the actual production capacity of horizontal wells cannot meet the expected plan. − The main fluid-sensitive minerals in shale are clay minerals. − The high content and diverse...…”

“…31 − 35 Intrusion into the solid phase can cause reservoir fractures and pore throat plugging, while intrusion into the liquid phase is prone to sensitivity damage and water-phase trap damage. 36 − 39 The depth of drilling fluid intrusion and the degree of damage increase with the increase of positive differential pressure in the wellbore and drilling time. 40 − 44 Among them, as an important development direction of oil and gas wells, it is crucial to study the damage factors and extent of horizontal wells.…”

Fine Modeling of Multiscale Fracture Cavity Fusion in Fault Solution Reservoirs Based on Multiscale Discrete Crack Modeling Method

“…Marinković et al conducted a composite hydrogeothermal investigation of the post-Neotethys Late Paleogene Neogene crustal core complex in the Kopaonik Mountains of the southwestern Serbian Plateau. The fractured carbonate reservoirs in Tahe Oilfield are different from conventional porous sandstone reservoirs and other karst carbonate reservoirs. − The main storage space of oil reservoirs is mainly composed of cracks and caves formed by structural deformation and collapse, as well as pores and caves formed by karst processes. − The large karst caves are the most important storage space, and cracks are the main connecting channels. − Due to the different types of karst caves and cracks of different scales, their morphology and scale are different, making it difficult to establish a unified geological model using a single method. − Therefore, different modeling methods are used to establish discrete models for different constituent elements. − Then, the discrete models were integrated into a wpore, establishing a three-dimensional distribution model of the fractured and vuggy reservoir. − …”